This invention relates to a ball-screw mechanism and assembly.
In a conventional ball-screw assembly, a nut body is mounted on a shaft, the shaft having a continuous helical groove on its surface, and the inner surface of the nut having a corresponding groove. Between the nut and shaft are disposed a number of balls that recirculate in an endless path defined by the grooves and a ball transfer bore provided in the nut. Such a known conventional ball-screw assembly is used in many applications to convert linear motion to rotary, and vice versa.
In such a conventional assembly, for the nut to be adequately supported by the balls, the axial length of the recirculating ball path must extend for at least two turns of the helical groove. Thus the minimum length of the nut is dependant on the pitch of the groove. However the length of the nut cannot simply be reduced at will by reducing the pitch of the groove; once the pitch is reduced, the angle that the groove makes to the axis of the shaft is increased, and this increases the frictional resistance to the relative rotation of the nut and shaft.
For many applications this problem is not important since the size of the nut is not critical. In other applications, however, where the size and weight of the nut are important factors, the difficulty of providing a small nut that will still run smoothly on the shaft has proven to be disadvantageous.